1. Field of the Invention
Embodiments of the present invention relate generally to a display device and, more specifically, to an optical component calibration system for a laser-based display device.
2. Description of the Related Art
Electronic display systems are commonly used to display information from computers and other sources. One well-known type of display device is a cathode-ray tube (CRT) display. A CRT display includes one or more electron guns that accelerate electrons towards an inner surface of a display screen. A layer of phosphors disposed on the screen phosphoresces when impacted by the electrons, causing visible light to emanate from an outer surface of the screen. The CRT display also includes a set of magnetic coils that deflect the trajectory of the electrons emitted by, the electron gun in order to cause the electrons to impact specific positions on the inner surface of the display screen. The resulting visible light forms an image on the outer surface of the display screen. CRT displays usually require calibration in order to function properly. For example, the magnetic coils must be configured to deflect the electrons onto specific positions on the inner surface of the screen and not onto any other region within the CRT display.
In some modern devices, a laser beam or multiple laser beams are used to excite phosphor material-containing regions (pixels) of a display screen instead of an electron gun. In such devices, a laser module transmits a laser beam towards a spinning polygon having a plurality of mirrored facets. As the polygon rotates, the different facets reflect the laser beam towards the display screen. The laser module transmits the laser beam towards the polygon during particular time intervals so that the laser beam is reflected only towards the display screen, and not reflected towards any off-screen regions. Since the polygon rotates at several thousands of revolutions per minute and since the phosphor pixels are small, the laser module must pulse the laser beam with precise timing with a very small margin for error. Due to the small margin for error, calibrating the activation timing of the laser module can be difficult and unreliable.
A system for calibrating the activation timing of excitation laser beams in a laser module is disclosed in U.S. Patent Application Pub. No. 2010/0097678, entitled “Servo Feedback Control Based on Designated Scanning Servo Beam in Scanning Beam Display Systems with Light-Emitting Screens.” In this system, a non-imaging servo beam is directed at calibration features disposed on a display screen and reflected towards an optical sensor. The optical sensor produces feedback signals indicative of positioning of the non-imaging servo beam in relation to the display screen. The activation timings of the excitation beams are then adjusted relative to the activation timing of the non-imaging servo beam to control the alignment of the excitation beams relative to the display screen.
Even after the display device is calibrated in the above manner, the optical components of the display device may go out of calibration during use as a result of drift, e.g., due to changes in temperature. To correct for this drift, the user could wait until the laser-based display device is not being used and perform the calibration described above at that time. However, this may not be practical because some display devices are used continuously over many hours. Also, the onset of some drift effects may occur quite rapidly and before a user has an opportunity to recalibrate the display device in the above manner. Therefore, what is needed in the art is a calibration technique for a laser-based display device that compensates for drift during user operation of the display device while maintaining the quality of the displayed image.